As the ability of semiconductor manufacturers to reduce the physical size of circuits has improved, the power dissipation in the circuits so manufactured has accordingly increased. As a result, it has become increasingly necessary to provide some form of cooling for integrated circuit chips and modules. In relatively low circuit density applications, forced air with suitable space air conditioning has proved to be sufficient. However, as circuit density increases, the heat dissipation requirements increase as well. In such environments, more effective cooling techniques than using forced air are required. The higher efficiency cooling techniques that have been used frequently include the use of water cooling and the like. Various cooling devices are also required to transfer the heat form its source on a chip to a water cooling jacket.
While it is well understood that in situations involving high circuit density that effective cooling is required in order to maintain chip operating temperatures at acceptable levels, the techniques available for measuring the thermal performance of various cooling approaches has not proved to be as accurate as is desired. As a consequence, design of suitable cooling systems typically have required a great deal of over capacity in order to assure that the desired operating chip temperature is not exceeded.
Various approaches are known in the prior art for measuring heat flow. One such approach is illustrated in U.S. Pat. No. 3,720,103 which relates to a heat flux meter. In that device, thermocouples are used to measure the temperature differential between two surfaces. The sensed temperature difference controls a heater which is adjusted so that heat flow between the surfaces is prevented. The first surface is shielded from the environment to prevent heat flow therefrom to this surface. This device, however, is not suitable for measuring the performance of a cooling device such as a heat sink or heat transfer device used in a semiconductor module for cooling a semiconductor chip or the like.
A method and apparatus for determining the thermal resistance in semiconductors is illustrated in U.S. Pat. No. 3,745,460. In this approach, a current pulse is fed into the semiconductor causing heat to be generated therein. The detected time interval between cessation of the pulse and detection of maximum heat transfer leads to a determination of the thermal resistance.
A method and apparatus for determining the heat transfer characteristics of a tube is described in U.S. Pat. No. 4,396,300. The apparatus includes an electric heater for heating a block which surrounds and engages part of the tube. A liquid is pumped through the tube and a thermistor is used to measure the fluid temperature. A pressure drop sensor is provided to sense the drop in pressure across the block. The sensed data is transferred to a computer for computing the heat transfer resistance. Like the other approaches mentioned above, this method too is not suitable for determining the effectiveness of a heat transfer device used in a module to cool a semiconductor chip.